MOUNTAINSIDE — The eerie blue light and loud folk-rock pouring from the old brick church last Sunday seemed to belie the conservative evangelical doctrine that Mountainside Chapel’s members have adhered to for nearly two centuries.

But more important to the congregation that night was a different spectacle on display — people, hundreds of them, all there to pray and sing and reinvigorate a church community that had been on its last legs.

Mountainside Chapel, founded in 1821 and known for many years as Mountainside Gospel Chapel, has merged with Liquid Church, a youth-driven congregation whose leaders say is growing by 20 percent each year. Liquid Mountainside will hold its first services in the revamped chapel today.

The two groups consider the merger a win-win: Mountainside Chapel, which elders said had been losing members steadily in recent decades, will get an influx of excited young Christians, while Liquid will get its first permanent location in the church’s six-year history.

The building and accompanying land, located just off Route 22, are valued at around $4 million. The entire property was donated to Liquid Church.

Liquid founder and lead pastor Tim Lucas said the timing was uncanny. In April 2012, his staff met with Warren Bird, author of “Better Together: Making Church Mergers Work,” and Bird gave him the book and told him a merger could be in Liquid’s future.

Lucas said he put the book aside, thinking it would never happen. At 7 a.m. the next day, he got a phone call — it was Mountainside, asking if Liquid would be interested in making their chapel the church’s newest campus.

SAME MESSAGE, NEW METHODS

Mountainside Chapel has a long history in Union County. Originally Locust Grove Sunday School in Westfield, it later moved to Route 22, where its location earned it the nickname “The Church of the Highway.” When the traffic got too severe, the state asked the church to move to its current location, where it enjoyed a heyday through the 1980s, with more than 200 families attending regularly.

“Our kids got older, started getting married and moving away, and you lose members to death, so our numbers just kept dwindling down, to the point where it started to get a little financially difficult for us,” said Joe Krasen, a church elder. “We probably had another one, two years, and then it would have been extremely difficult.”

By 2012 the church had 30 regular families attending, not even enough to keep up with maintenance costs.

“For five years prior to this I had been contacting people asking if there had been any good church mergers, and they said, no, not really. Because it’s usually two failing churches coming together,” said Dr. Gregg Hagg, Mountainside’s longtime pastor.

Hagg said he knew about Liquid from his son, who was part of the church at its beginning.

“We knew it was one of the strongest, youngest, most vibrant congregations around,” Hagg said. “We didn’t want to just hand something over to the next generation, we wanted to join the next generation.”

The church elders said they expected a bit of resistance from the older congregants, but when it came time to vote on giving away the property and merging with Liquid, support was unanimous.

“I’ve been in ministry for about 45 years now, and I’ve never witnessed anything quite like this,” Hagg said. “So I’ve been telling people, we’re either the biggest fools, or God’s really doing something special here, and I choose to believe the latter.”

‘CONTINUING A MISSION’

For years, Liquid has operated as three remote campuses. Each Sunday morning, they set up gear at the Hyatt in Morristown, the Heldrich in New Brunswick, and John Walker Middle School in Nutley, and pack it all up again by the end of the day.

Lucas started the church in 2007, a few years after quitting his job as an English teacher at Summit High School. When Liquid launched in Morristown, there were 300 members, Lucas said. That number is now closer to 3,000.

“Our main saying is faith is a journey, not a guilt trip, and I think a lot of people in New Jersey are skeptical of organized religion,” Lucas said. “We’re not gonna try to convert you, or arm-twist, or demonize people, we don’t do that. And I think that’s refreshing to people.”

During the summer, Liquid remodeled the Mountainside church from top to bottom. The sanctuary, once filled with pews and large stained-glass windows, now features two massive TVs on either side of a movie screen, along with professional lighting and sound systems more suited for a concert venue.

The building also has nurseries, classrooms and communal rooms, all decked out with modern furniture and bright paint jobs. In the basement, the old stained glass from the sanctuary has been installed into a wall, which Lucas said is an important reminder of the building’s history.

“As a young contemporary church, we realized that with the spiritual roots here, we’re not starting a new ministry, we are continuing a mission that’s been going on for almost 200 years,” he said. “So we do that with a lot of humility and reverence.”

Perhaps most unique to Liquid are the “chill spaces” — rooms specially designed for children with autism, where they can work one-on-one with specially trained volunteers each week while their parents attend the service.

At the launch event last Sunday, Liquid volunteers in horn-rimmed glasses, fedoras and Toms sneakers mingled with white-haired Mountainside Chapel regulars in the foyer as the house band played music that sounded like a Christian-tinged Mumford & Sons.

“Where did all these people come from?” joked Gloria Schmey, who has been a member of Mountainside Chapel for decades.

“It looks very warm and friendly, they’ve done an excellent job,” said longtime Mountainside member Ruth Goense, as she and a group of older congregants winced a bit at the volume of the music.